Depends on where you're at. In the US, there is no such thing as an air brake endorsement - only a restriction for CDL drivers who don't both pass the written air brakes test and perform their road test in a vehicle so equipped. In other countries, there is such an endorsement.
No such thing as an air brake endorsement on a US license.
No, because there is no such thing as an air brake endorsement on a US license.
In some countries, to be permitted to operate an air brake equipped vehicle, your licence must show an endorsement which permits you to. In the US, "air brake endorsement" is actually a misnomer - there is no air brake endorsement on a US licence. If a CDL driver does not pass the written air brakes test and conduct their road test in an air brake equipped vehicle, they get a restriction prohibiting them from operating an air brake equipped commercial vehicles. However, this is only applicable to commercial vehicles - operating a non-commercial vehicle with air brakes requires absolutely no qualification, whatsoever.
Yes, in Michigan, you are required to have an air brake endorsement to drive a commercial vehicle with air brakes. This endorsement is obtained by passing a written knowledge test specifically for air brake systems.
You can't get one, because such an endorsement does not exist.
No. Such an endorsement does not exist for US licenses.
There is no such thing as an air brake endorsement on any license in any US state or territory.
No. There is no air brake endorsement. If you completed the written air brakes test and did your road test in a vehicle equipped with air brakes, you're certified to operate an air brake equipped CMV. Otherwise, you'll have a restriction on your license which prohibits you from operating a CMV equipped with air brakes (although this does not apply to non-CMVs, such as U-Haul trucks and RVs).
Only if it's either designed to transport more than 15 persons (including the driver), or else carrying a quantity of hazardous materials which requires the display of placards under the FMCSR. In both instances, you would need at least a Class C CDL without an air brake restriction (there is no actual air brake endorsement), as well as a passenger endorsement (for a passenger bus) or hazardous materials endorsement.
Such an endorsement does not exist - there is only an air brake restriction. Basically, if you're operating any vehicle requiring a CDL, you cannot operate that vehicle with that restriction if it is equipped with air brakes. For vehicles under 26,000 lbs. GVWR, this would include any vehicle carrying hazmat, or any bus designed to transport more than 15 persons (including the driver).
You can't get an air brake endorsement ANYWHERE in the US on ANY class of license, because it doesn't exist.
Air brake endorsements fall under Federal laws so every state will have the same minimum requirement for an air brake endorsement if you have air brakes on your vehicle.